1. Field of the Invention
The present invention relates generally to pressure vessels that include an end element that is bonded or welded to a cylindrical tube, and more particularly to reciprocating fluid devices of the type having a welded tube and end element assembly.
2. Description of the Prior Art
Reciprocating fluid devices including single action cylinders, double action cylinders, shock or energy absorbers, and piston type accumulators have often included a bond or weld to attach an end element or base to the barrel or cylindrical tube; since a bonded or welded construction is more attractive and consumes less mounting space than older constructions that utilize tie bolts between the base and head of the cylinder.
Operating pressures for these types of fluid devices, when used in hydraulic systems, often are in excess of 2500 psi, and in some applications are in excess of 6000 psi. Thus the bond or weld between the tube and base is subjected to high cyclic stresses. In addition, in many applications the fluid device is subjected to fluid pressures that are higher than the operating pressure of the hydraulic system due to gravity or inertia loading or to the geometry of mechanical linkages which use the forces of one hydraulic cylinder to place a greater load on another hydraulic cylinder.
The failure in a bonded joint, whether of brazed or welded construction, has been caused by cyclic and fluid pressure induced stresses in the brazed joint or weld by resultant cyclic elastic diametral tensile strains in the barrel or cylindrical tube at a location longitudinally proximal to the bond or weld. These elastic diametral tensile strains have induced bending stresses in the bond or weld that are additive to cyclic and fluid pressure induced longitudinal stresses in the weld.
The welding of the base to the cylindrical tube is customarily arc welded by an automatic machine that feeds a fluxless wire into the weld; and oxygen is excluded from the molten material either by an envelope of inert gas or by a granular flux which submerges the arc.
Some designs have utilized brazing for attaching the bases to the cylindrical tubes; and, because of the lower temperatures that are required and the need to restrict the heating of the tube to a localized area, silver alloy brazing materials have been used in preference to copper.